Apparatus and method for measuring the molten metal level in electromagnetic continuous casting

ABSTRACT

An apparatus and method for measuring the level of a free surface of molten metal in an electromagnetic continuous casting process using an AC electromagnetic field. A detection coil is provided to detect the sum of a magnetic field applied from an induction coil and an induced magnetic field based on eddy current in the molten metal. An arithmetic unit is provided to detect the surface level of the molten metal by removing a variation of the applied magnetic field with a variation in current to the induction coil from an output signal from the detection coil. The surface level of the molten metal can be accurately measured by determining whether a variation in the output of the detection coil results from a variation in the applied magnetic field or a variation in the surface level of the molten metal.

TECHNICAL FIELD

The present invention relates in general to an apparatus and method formeasuring the level of molten metal in an electromagnetic continuouscasting process, and more particularly to an apparatus and method formeasuring the level of the surface of molten metal in an electromagneticcontinuous casting process using an alternating current (AC)electromagnetic field.

BACKGROUND OF THE INVENTION

As well known to those skilled in the art, an electromagnetic continuouscasting process is a technique for applying an electromagnetic fieldacross the surface of molten metal and casting the molten metal using anelectromagnetic force and Joule heat induced due to the appliedelectromagnetic field. In this technique, a part of the molten metal tobe initially solidified is heated by the Joule heat and then slowlycooled, resulting in the formation of a thin, initial solid shell underthe surface of the molten metal, thereby making it difficult to form anoscillation mark (OM). Further, because a contact angle between acasting mold and the molten metal surface is increased due to theelectromagnetic force, the initial solid shell is less influenced by amold oscillation, resulting in an improvement in surface characteristicof a cast product. On the other hand, such an electromagnetic continuouscasting process is adapted to apply a strong AC electromagnetic fieldacross a free surface (referred to hereinafter as surface) of the moltenmetal differently from existing processes, which field is induced byapplying AC current to an induction coil installed in a place outsidethe casting mold where the molten metal surface is to be positioned.

In the above-mentioned electromagnetic continuous casting process, thesurface of the molten metal is an important factor in determining thesurface state of a cast product and must thus be finely controlled tomaintain the surface state of the cast product better. For this reason,it is very important to accurately measure the surface level of themolten metal. In the case where the surface of the molten metal isbeyond a desired level, a remarkable OM is formed on the surface of acontinuous cast product, which may lead to a serious defect in thesubsequent process. In this regard, the surface level of the moltenmetal in the electromagnetic continuous casting process must be morestrictly managed than in general casting processes. It is generallyknown in the art that the surface characteristic of a cast product ismost excellent when the surface of the molten metal has the same heightas that of the top end of the induction coil.

For measuring the surface level of molten metal in existing steelcontinuous casting processes, there have conventionally been proposed amethod using radioactive rays incapable of being transmitted through themolten metal, a method using an eddy current sensor (see U.S. Pat. No.4,567,435, 1987), a method using an electrostatic capacity sensor (seeU.S. Pat. No. 4,555,941, 1985), etc. However, these methods cannot beused for the electromagnetic continuous casting process where a strongAC electromagnetic field is present on the surface area of the moltenmetal, because their measuring devices are subjected to heating orrestrictions in space. The method based on the eddy current sensor isdesirable to finely measure the surface level of the molten metal, butdisadvantageous in that the eddy current sensor is positioned within amold. Namely, when a strong electromagnetic field is applied to thesurface area of the molten metal as in the electromagnetic continuouscasting process, the eddy current sensor is magnetically saturated andthus loses its function as the sensor. The method based on theelectrostatic capacity sensor is subjected to a strict restriction inspace because no conductive material having an effect on electricpotential must be present within the range of a distance between anelectrode and the surface of the molten metal. Further, because theelectrostatic capacity sensor is considerably influenced by a dielectricconstant of powder in the surface of the molten metal in casting themolten metal, its output varies with the thickness of the powder,resulting in the generation of an error within a very wide range.Moreover, a conductive material, which has to be installed relativelynear the surface of the molten metal, may be induction-heated by thestrong electromagnetic field in the electromagnetic continuous casting,thereby causing it not to act as the sensor. Similarly, in the methodbased on the radioactive rays, a proposed device cannot perform its ownfunction due to the induction heating by the electromagnetic field.

For measuring the surface level of molten metal in the electromagneticcontinuous casting process, there have conventionally been available amethod using a frequency variation of an external induction coil forapplying an electromagnetic field (see U.S. Pat. No. 4,446,562, 1984), amethod using an inductance variation of an induction coil (see JapanesePatent Laid-Open Publication No. Heisei 6-122056), etc. An electric loadin electromagnetic continuous casting equipment including an inductioncoil, a casting mold, molten metal, etc. basically varies with thesurface level of the molten metal. As a result, there are variations ina voltage from a power supply device to the induction coil andassociated current, inductance and frequency. The above methods areadapted to measure the surface level of the molten metal using such aphenomenon. However, the measuring performance is excellent when thesurface of the molten metal is within the range of the induction coil,but abruptly degraded when the surface of the molten metal is beyond therange of the induction coil. This requires a band for measurement of thesurface level of the molten metal to be limited to the range of theinduction coil.

One approach to such a problem is the extension of the surface levelmeasuring band by an auxiliary coil installed above the induction coil.In this approach, however, the measuring band is limited to a rangedefined by the two coils, too (see Iron and Steel, Vol. 84, p 625,1998). In a method of measuring an inductance variation of an inductioncoil using a detection coil, shown in Japanese Patent Laid-OpenPublication No. Heisei 6-122056, values measured by the detection coilinvolve influences resulting from voluntary variations in current to theinduction coil with casting conditions. As a result, it is unreasonableto apply the measured values to the accurate measurement of the surfacelevel of the molten metal without correcting such variations.

Another approach is a method using a magnetic field sensor (see KoreaPatent Application No. 99-28920), which is applicable to the measurementof the surface level of molten metal in the electromagnetic continuouscasting process in that the magnetic field sensor has an excellentsensitivity and a wide detection band. However, a considerable degree oferror may occur in the measured result in the case where current to aninduction coil is severe in variation.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide an apparatus and method for measuring the levelof the surface of molten metal in an electromagnetic continuous castingprocess, which can effectively remove noise components generated from apower supply device of an electromagnetic continuous casting machine andexternal noise components, accurately measure the surface level of themolten metal and provide molten metal surface level data appropriate toother equipment in accordance with the accurate measurement.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by a provision of an apparatus formeasuring the level of the surface of molten metal within a mold in anelectromagnetic continuous casting process by detecting a magnetic fieldapplied from an induction coil and an induced magnetic field based oneddy current in the molten metal, comprising power supply means forsupplying predetermined AC power to the induction coil and setting apower variable indicative of a variation in the AC power; a detectioncoil for detecting the sum of the applied magnetic field from theinduction coil and the induced magnetic field; amplification/filteringmeans for amplifying an output signal from the detection coil to apredetermined level and filtering the amplified signal to remove noisecomponents therefrom; and an arithmetic unit responsive to an outputsignal from the amplification/filtering means and the power variablefrom the power supply means for detecting the surface level of themolten metal by removing components of the applied magnetic field basedon the variation in the AC power to the induction coil from the magneticfield sum detected by the detection coil.

In accordance with another aspect of the present invention, there isprovided a method for measuring the level of the surface of molten metalwithin a mold in an electromagnetic continuous casting process bydetecting the sum of a magnetic field applied from an induction coil andan induced magnetic field based on eddy current in the molten metalthrough a detection coil, comprising the first step of amplifying anoutput signal from the detection coil to a predetermined level andfiltering the amplified signal to remove noise components therefrom; andthe second step of determining the surface level of the molten metal byremoving components of the applied magnetic field based on a variationin current to the induction coil from the amplified and filtered signal.

DETAILED DESCRIPTION OF THE INVENTION

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view showing the construction of an apparatus for measuringthe level of the surface of molten metal in an electromagneticcontinuous casting process in accordance with the present invention;

FIG. 2 is a block diagram showing the construction of level detectionmeans in FIG. 1;

FIG. 3 is a graph showing variations of a magnetic field applied to themolten metal and a magnetic field induced in the molten metal by theapplied magnetic field in accordance with the present invention;

FIG. 4 is a graph showing the measured results of the surface level ofthe molten metal based on current variations of an induction coil inaccordance with the present invention; and

FIG. 5 is a graph showing an example of the measured results of thesurface level of the molten metal in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a view schematically showing the construction of an apparatusfor measuring the level of the surface of molten metal in anelectromagnetic continuous casting process in accordance with thepresent invention. As shown in this drawing, the surface levelmeasurement apparatus comprises an induction coil 3 installed apart froma mold 1 for generating a magnetic field in response to AC currentapplied thereto and applying the generated magnetic field to moltenmetal 4 within the mold 1, a power supply device 7 for applying the ACcurrent to the induction coil 3, a detection coil 6 for detecting themagnetic field generated by the induction coil 3 and a magnetic fieldinduced by eddy current generated in the molten metal 4 according to theapplied magnetic field, and level detection means 8 for detecting thesurface level of the molten metal 4 from the sum of the magnetic fieldsdetected by the detection coil 6.

Preferably, the power supply device 7 may apply AC current of severalten to several hundred KHz and several thousand A to the induction coil3. Further, the magnetic field generated by the induction coil 3 and themagnetic field induced by the eddy current generated in the molten metal4 may be AC magnetic fields of the same frequency.

If the power supply device 7 applies the AC current to the inductioncoil 3, then the induction coil 3 applies a magnetic field to the moltenmetal 4 through the mold 1, resulting in the generation of eddy currentin the molten metal 4 and, in turn, the generation of an inducedmagnetic field based on the eddy current. The detection coil 6 measuresthe sum of the applied magnetic field and induced magnetic field anddetects the surface level of the molten metal in accordance with themeasured result.

The level detection means 8 removes noise components from a leveldetection signal from the detection coil 6 and measures the surfacelevel of the molten metal on the basis of the noise-removed leveldetection signal. The level detection means 8 is further adapted tostably control the surface level of the molten metal for the stableformation of a solid shell, thereby improving the surface quality of acast product.

The detection coil 6 may preferably be configured to measure a magneticfield parallel to the axis of the mold 1, a magnetic field perpendicularto the mold axis or the combination of the magnetic fields parallel andperpendicular to the mold axis. In order to detect such a magneticfield, the detection coil 6 may preferably be installed at a positionoutside the upper portion of the mold 1 or at a position above theinduction coil 3 (i.e., at a position around the upper portion of themold 1). Although the detection coil 6 is shown in the preferredembodiment of the present invention to be installed at a position aroundthe upper portion of the mold 1, those skilled in the art willappreciate that the detection coil 6 is not limited to such a position.

FIG. 2 is a block diagram in detail showing the construction of thelevel detection means 8 in FIG. 1. As shown in this drawing, the leveldetection means 8 includes an isolation amplifier 9 for amplifying anoutput signal from the detection coil 6 to a predetermined level.Noticeably, an external high noise may be introduced in the detectioncoil 6 because the coil has a coiled shape, and a general differentialamplifier cannot remove a common mode noise of 10V or more. In thisregard, the isolation amplifier 9 may preferably be used for systemprotection and stable amplification.

It should also be noted that it is necessary to acquire only signalcomponents within a specific frequency range required for levelmeasurement from an output signal from the isolation amplifier 9 becausethis signal contains noise components resulting from electricalfluctuations of the power supply device. For this reason, a band passfilter (BPF) is provided to remove noise components from the outputsignal from the isolation amplifier 9. An output signal from the BPF 10still has an AC signal characteristic. In order to utilize such a signalfor the control of the surface level of the molten metal, a directcurrent (DC) signal converter 17, which is composed of either a rootmean square (RMS) calculator 11 or a peak detector 12 must be used toconvert that signal into a DC signal within a predetermined period oftime. An output signal from the RMS calculator 11 or peak detector 12still has high-frequency noise components. In this regard, a low passfilter (LPF) 13 is used to remove noise components from the outputsignal from the RMS calculator 11 or peak detector 12. The noise-removedsurface level detection signal from the detection coil 6 may betransmitted by long distance according to a given condition. To thisend, a differential output converter 14 is used to amplify an outputsignal from the LPF 13 to a predetermined level. An analog/digital (A/D)converter 15 is adapted to convert an analog output signal from thedifferential output converter 14 into a digital signal. As a result, theA/D converter 15 sends a signal with no noise component to an arithmeticunit 16.

The arithmetic unit 16 is adapted to determine the surface level of themolten metal on the basis of the measured value from the detection coil6, converted into the digital signal by the A/D converter 15. Herein,the detection coil 6 is adapted to detect the surface level of themolten metal according to the principle as will hereinafter be describedin detail.

The fundamental principle of the detection coil 6 is to useelectromagnetic induction. Namely, an AC magnetic field is applied tothe molten metal using a power supply device of an electromagneticcontinuous casting machine and an induced magnetic field is generated inthe molten metal by means of the applied AC magnetic field. Then, thedetection coil 6 measures the surface level of the molten metal bydetecting the sum of the applied magnetic field and induced magneticfield.

If a magnetic field varying with time is applied across a conductivematerial, then an electromotive force ε is generated in the conductivematerial due to a magnetic field B perpendicular to the material, as inthe below equation 1. Then, an induced current circuit obeying the Ohm'slaw is formed on a circuitry where the electromotive force is generated.$\begin{matrix}{ɛ = {{- \frac{}{t}}{\int_{c}{{B \cdot n}\quad {a}}}}} & \lbrack {{Equation}\quad 1} \rbrack\end{matrix}$

The direction of an induced magnetic field generated by induced currentvaries with that of an external magnetic field which is applied to aconductive material to maintain the induced magnetic field constant inthe conductive material. That is, the direction of the induced magneticfield is opposite to that of the applied magnetic field, as seen from aminus sign in the above equation 1.

The detection coil 6 may preferably be a search coil-type magneticsensor for measuring a magnetic field by measuring an electromotiveforce induced therein. Namely, the detection coil 6 measures the surfacelevel of the molten metal by measuring an induced magnetic field basedon a current loop formed in the surface of the molten metal. Atime-variation rate of a magnetic flux crossing an area surrounded bythe detection coil 6 is the sum of a time-variation rate of an appliedmagnetic field B^(e) _(p) based on current through the induction coiland a time-variation rate of an induced magnetic field B^(i) _(p) basedon current induced in the molten metal. As a result, the output (V1) ofthe detection coil 6 can be expressed by the following equation 2.$\begin{matrix}{{V1} = {{- \frac{}{t}}{\int_{c}{{( {B_{p}^{e} + B_{p}^{i}} ) \cdot n}\quad {a}}}}} & \lbrack {{Equation}\quad 2} \rbrack\end{matrix}$

The magnetic field sum, measured by the detection coil 6 in the abovemanner, is amplified to a predetermined level and noise-removed by theabove-mentioned amplification and filtering means and then transferredto the arithmetic unit 16 for the determination of the surface level ofthe molten metal.

The arithmetic unit 16 removes the components of said applied magneticfield induced due to the variation on the current applied by the powersupply device from the magnetic field sum detected by said detectioncoil on the basis of the below equation 3 to detect the surface level ofthe molten metal depending on, not a variation of the applied magneticfield but a variation in position of the surface of the molten metal.$\begin{matrix}{{{SURFACE}\quad {LEVEL}} = {\frac{1}{k}\lbrack {{- \ln}\frac{a - V_{1}}{a - b}} \rbrack}^{\frac{1}{d}}} & \lbrack {{Equation}\quad 3} \rbrack\end{matrix}$

In the above equation 3, a=C1*V2+C2, b=C3*V2+C4, d=C5*V2+C6, k=C7,V1=magnetic field sum and C1, C2, C3, C4, C5, C6 and C7=constantsassociated with the value of V2. V2 is directly related to the power orthe current applied to the induction coil. In other words, in the aboveequation 3, the variable a represents the lowest surface level (forexample, 300 mm) of the molten metal in a detection area of thedetection coil 6, the variable b represents the highest surface level(for example, 0 mm) and the variable d represents the surface level whenthe slope of an induced magnetic field graph, which will be mentionedlater in detail, is k.

A strong magnetic field induced by the induction coil is present in thesurface area of the molten metal according to the characteristic of theelectromagnetic continuous casting. In this connection, the detectioncoil concurrently measures a magnetic field applied by the inductioncoil and an induced magnetic field based on eddy current generated inthe molten metal.

As stated previously, an electric load in electromagnetic continuouscasting equipment and, thus, the amount of current from the power supplydevice to the induction coil vary with the surface position of themolten metal. As a result, there is also a variation in the appliedmagnetic field based on the induction coil current. The applied magneticfield is directly influenced by a variation in the amount of current tothe induction coil in the electromagnetic continuous casting process.For this reason, the applied magnetic field components must be removedfrom a magnetic field measured around the surface of the molten metal,to ensure that the surface level of the molten metal is accuratelymeasured in the electromagnetic continuous casting process.

On the other hand, the induced magnetic field contains both a componentvarying with the applied magnetic field when the surface of the moltenmetal is changed in position and a component varying with the surfaceposition of the molten metal even though the applied magnetic field isconstant. This signifies that the surface position of the molten metalcan be accurately detected by determining whether a variation in theoutput of the detection coil results from a variation in the appliedmagnetic field or a variation in the surface level of the molten metal.

In the present embodiment, a power variable V2 is used to correct avariation in the applied magnetic field based on a variation in theinduced magnetic field from the output of the detection coil. The V2 isa variable capable of being representative of the applied magnetic fieldand provided from the power supply device supplying power to theinduction coil. Also, the power variable V2 is irrelevant to a variationin surface position of the molten metal and a variation in electric loadin the electromagnetic continuous casting process and one-to-onecorresponds to a current value impressed on the induction coil. Thepower variable V2 may preferably be set to AC current, voltage or powerthat the power supply device supplies to the induction coil.

FIG. 3 is a graph showing the comparison between a variation in theapplied magnetic field and a variation in the induced magnetic fieldwith a variation in the surface position of the molten metal. As shownin this drawing, the applied magnetic field is narrow in detection bandwhereas the induced magnetic field is wide in detection band.

As seen from the above equation 3, the power variable V2 from the powersupply device is contained respectively in the variables a, b and d.This makes it possible to remove influences of a variation in theapplied magnetic field with a voluntary variation in the induction coilcurrent depending on a given casting condition and a variation in theapplied magnetic field with a variation in the surface position of themolten metal. In other words, in the present embodiment, the arithmeticunit measures the surface position of the molten metal by separatingonly the value of a variation in the induced magnetic field resultingfrom a variation in the surface position from the output signal from theA/D converter. Hence, the arithmetic unit can stably measure the surfacelevel of the molten metal even though the amount of induced current tothe induction coil voluntarily varies in the electromagnetic continuouscasting process as needed.

FIG. 4 is a graph showing the measured results of the surface level ofthe molter metal based on current variations of the induction coil inaccordance with the preferred embodiment of the present invention. Inthe case where a regulated voltage or current, which is one of selfelectrical signals of the power supply device, is extracted and appliedto the level detection means, an abrupt variation in current to theinduction coil or an abrupt variation in the applied magnetic field hasno effect on the measured results of the surface level of the moltenmetal as seen from FIG. 4. It can also be seen from FIG. 4 that thesurface position of the molten metal slowly varies within the range of80 to 90 mm. This is based on the fact that the surface position of themolten metal varies through the process to prevent a nozzle forinjection of the molten metal from being corroded.

FIG. 5 is a graph showing an example of the measured results of thesurface level of the molten metal in accordance with the presentinvention. As shown in this drawing, the measured level value has animproved noise value of about 0.3 mm in the present case as comparedwith a noise value of about 4 mm in the conventional case. Therefore, itcan be seen that the level measurement accuracy has been significantlyenhanced according to the present invention. On the other hand, a signaloscillates on the order of once a second after the present invention isapplied to the level measurement. Such a signal is based on theself-oscillation of the mold and represents a variation in the surfacelevel of the molten metal.

As apparent from the above description, according to the presentinvention, the surface level of molten metal can be accurately measuredirrespective of variations in current and voltage from a power supplydevice to an induction coil by removing components of an appliedmagnetic field from the induction coil from the output of a detectioncoil detecting the applied magnetic field and an induced magnetic fieldbased on a variation in surface position of the molten metal.

Further, according to the present invention, the surface level of themolten metal can be stably measured at a high accuracy and thus used asa reference signal for the surface level control. Therefore, the surfacequality of a cast product can be increased, thereby reducing the lengthof a manufacturing process for steel products and saving energy.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. An apparatus for measuring the level of thesurface of molten metal within a mold in an electromagnetic continuouscasting process by detecting a magnetic field applied from an inductioncoil and an induced magnetic field based on eddy current in the moltenmetal, comprising: power supply means for supplying predetermined ACpower to said induction coil and setting a power variable indicative ofa variation in the AC power; a detection coil for detecting the sum ofsaid applied magnetic field from said induction coil and said inducedmagnetic field; amplification/filtering means for amplifying an outputsignal from said detection coil to a predetermined level and filteringthe amplified signal to remove noise components therefrom; and anarithmetic unit responsive to an output signal from saidamplification/filtering means and said power variable from said powersupply means for detecting the surface level of said molten metal byremoving components of said applied magnetic field induced due to thevariation in said AC power applied to said induction coil from saidmagnetic field sum detected by said detection coil.
 2. The apparatus asset forth in claim 1, wherein said amplification/filtering meansincludes: an isolation amplifier for amplifying the output signal fromsaid detection coil to said predetermined level; a band pass filter forfiltering only signal components of a predetermined band from an outputsignal from said isolation amplifier; a DC signal converter forconverting an output signal from said band pass filter into a DC signal;a low pass filter for filtering the DC signal from said DC signalconverter to remove noise components therefrom; and an analog/digitalconverter for converting an analog output signal from said low passfilter into a digital signal and outputting the converted digital signalto said arithmetic unit.
 3. The apparatus as set forth in claim 1,wherein said arithmetic unit is adapted to detect the surface level ofsaid molten metal by removing the components of said applied magneticfield induced due to the variation in said AC power applied to saidinduction coil from said magnetic field sum detected by said detectioncoil on the basis of the following equation:${{SURFACE}\quad {LEVEL}} = {\frac{1}{k}\lbrack {{- \ln}\frac{a - V_{1}}{a - b}} \rbrack}^{\frac{1}{d}}$

where, a=C1*V2+C2, b=C3*V2+C4, d=C5*V2+C6, k=C7, V1=magnetic field sum,V2=power variable and C1, C2, C3, C4, C5, C6 and C7=constants.
 4. Theapparatus as set forth in claim 1, wherein said power supply means isadapted to set said power variable according to the variation in said ACpower to said induction coil, said power variable being irrelevant to avariation in surface position of said molten metal and a variation inelectric load in said electromagnetic continuous casting process andone-to-one corresponding to a current value impressed on said inductioncoil.
 5. The apparatus as set forth in claim 1, wherein said detectioncoil is in stalled at a position around an upper portion of said mold.6. The apparatus as set forth in claim 1, wherein said detection coil isconfigured to measure any one of a magnetic field parallel to the axisof said mold, a magnetic field perpendicular to said mold exist and thecombination of the magnetic fields parallel and perpendicular to saidmold axis.
 7. The apparatus as set forth in claim 3, wherein said powersupply means is adapted to set said power variable according to thevariation in said AC power to said induction coil, said power variablebeing irrelevant to a variation in surface position of said molten metaland a variation in electric load in said electromagnetic continuouscasting process and one-to-one corresponding to a current valueimpressed on said induction coil.
 8. The apparatus as set forth in claim5, wherein said detection coil is configured to measure any one of amagnetic field parallel to the axis of said mold, a magnetic fieldperpendicular to said mold axis and the combination of the magneticfields parallel and perpendicular to said mold axis.
 9. A method formeasuring the level of the surface of molten metal within a mold in anelectromagnetic continuous casting process by detecting the sum of amagnetic field applied from an induction coil and an induced magneticfield based on eddy current in the molten metal through a detectioncoil, comprising the steps of: a) amplifying an output signal from saiddetection coil to a predetermined level and filtering the amplifiedsignal to remove noise components therefrom; and b) determining thesurface level of said molten metal by removing components of saidapplied magnetic field induced due to a variation in current applied tosaid induction coil from the amplified and filtered signal.
 10. Themethod as set forth in claim 9, wherein said surface level determinationstep b) includes the step of detecting the surface level of said moltenmetal by removing the components of said applied magnetic field induceddue to the variation in said AC power applied to said induction coilfrom said magnetic field sum detected by said detection coil on thebasis of the following equation: $\begin{matrix}{{{SURFACE}\quad {LEVEL}} = {\frac{1}{k}\lbrack {{- \ln}\frac{a - V_{1}}{a - b}} \rbrack}^{\frac{1}{d}}} & \lbrack {{Equation}\quad 3} \rbrack\end{matrix}$

where, a=C1*V2+C2, b=C3*V2+C4, d=C5*V2+C6, k=C7, V1=magnetic field sum,V2=power variable from power supply means and C1, C2, C3, C4, C5, C6 andC7=constants.
 11. The method as set forth in claim 7, wherein said powersupply means is adapted to set said power variable according to avariation in AC power to said induction coil, said power variable beingirrelevant to a variation in surface position of said molten metal and avariation in electric load in said electromagnetic continuous castingprocess and one-to-one corresponding to a current value impressed onsaid induction coil.
 12. The method as set forth in claim 10, hereinsaid power supply means is adapted to set said power variable accordingto a variation in AC power to said induction coil, said power variablebeing irrelevant to a variation in surface position of said molten metaland a variation in electric load in said electromagnetic continuouscasting process and one-to-one corresponding to a current valueimpressed on said induction coil.